1. Field of the Invention
This invention relates to mortar compounds for setting tile and in particular for setting ceramic tile. More particularly, the invention relates to dry set mortar compositions which, in addition to being sag resistant, have high bond strength.
2. Description of the Prior Art
At present, tile and particularly ceramic tile is set in many cases by dry-set Portland cement mortars. Prior to the advent of dry-set mortars, the Portland cement compositions that were used had to be applied to the substrate in a very thick bed and generally also required a thin mortar coat for setting the tile. These thick bed mortar setting methods were referred to as mud-method tile setting systems. The mud-method Portland cement mortars have now been replaced to a great extent by thin-bed Portland cement dry-set mortars. Typical dry-set mortars are principally comprised of Portland cement, sand, and a water retentive cellulose ether, such as methyl cellulose or hydroxyethyl cellulose. The dry-set mortars are generally delivered to the job site in the dry state and water is added on the job site to mix the mortar into a slurry. U.S. Pat. No. 2,934,932 (Wagner; issued May 3, 1960) and U.S. Pat. No. 3,243,307 (Selden; issued Mar. 29, 1966) are illustrative of the dry-set mortars which are currently used to set tile in thin-beds. In addition, dry-set mortars can be provided with a rubber or polymer latex which is added to the dry mix to make a mortar which is then called a latex Portland cement mortar.
The dry-set mortars both with and without latex may also contain additives to provide or improve specific properties.
Originally, the dry-set mortars also contained asbestos fibers or similar fibrous materials which provided the mortar with the sag resistance. Sag resistance is a property or a characteristic relating to the ability of the mortar to resist movement under load until a certain load level is reached. This property or characteristic is vitally important in dry-set mortars and also to a latex mortar since a mortar, to be functional, must be in a slurry or paste form on the one hand, but also must be capable of supporting the load imposed on it by the tiles set in the mortar. It is therefore very important that the mortar support the tile without any appreciable slippage of the tile from the trowelled mortar surface during the period in which the mortar is setting. In wall applications, sag resistance is even more critical because the mortar must hold the tile in position on the wall during the period in which the mortar is setting. Sag resistance is defined by a test method that is part of the American National Standard Specification for Dry-Set Portland Cement Mortars-A1118.1.
Recently the tile industry, lead by the Tile Council of American Inc., has developed dry-set mortars which do not require the use of asbestos fibers. Rather than asbestos fibers, the dry-set mortars have been provided with other additives to afford sag resistance. U.S. Pat. No. 4,082,563 (Ellis et al; issued Apr. 4, 1978) discloses a dry-set mortar containing hydrated and anhydrous salts and similar ingredients to provide sag resistance rather than the asbestos.
Tile Council of America has also developed a superior asbestos-free dry-set mortar which contains long chain organic polymers. Anionic and nonionic long chain polyacrylamide materials are illustrative of the long chain organic polymers which provide the new improved mortar with sag resistant characteristics. The use of montmorillonite clays, attapulgite clays and mixtures of these clays have also been developed for use in mortars both alone and in combination with the long chain organic polymers. These developments are set forth in U.S. Pat. Nos. 4,021,257 (Bernett, May 3, 1977) and 4,043,827 (Bernett, Aug. 23, 1977).